This invention relates to a structure for connecting terminals, in which lands on a wiring board are connected with lead terminals on other substrate through solder or the like.
Conventionally, as such structure for connecting terminals, a structure of Prior Art 1 shown in FIG. 4 is known, for example.
In the structure of Prior Art 1, near-square-form rectangular lands 11 are arranged in a side-by-side manner on a wiring board by pitch of 0.5 mm. Rectangular lead terminals 21 on other substrate are superimposed on the lands 11. Long edges (long sides) 23,24 of the lead terminals 21 are longer than respective long edge 13,14 of the lands 11 by 0.1 mm, while short edges (short sides) 22 of the lead terminals 21 are shorter than respective short edges 12 of the lands by 0.1 mm.
As shown in the FIG. 4, the long edges 23,24 of the lead terminals 21 outwardly distanced from the respective long edges 13,14 of the lands 11 by 0.05 mm when the lands 11 and the lead terminals 21 are exactly in a designed position with each other. If the lands 11 and the lead terminals 21 are bonded through solder or similar conductive adhesives by automatic thermo-compression bonding in use of heat tool, fillets 5 of the solder or the like are formed on fringe portions on the lands 11 that outwardly protrude from the long edges 23,24 of the lead terminals 21.
The structure shown in the FIG. 4 is disadvantageous because even a 0.05 mm rightward or leftward deviation of the position of the lands 11 with respect to the lead terminals 21 makes the fillet 5 on right-hand side or left-hand side invisible from upper side through the other substrate, which has the lead terminals 21.
On the other hand, FIG. 5 shows another example of the conventional structure for connecting terminals, as designated as Prior Art 2.
In the structure of Prior Art 2, lands 11 as well as lead terminals 21, each of which is superimposed to respective one of the lands 11, are in a form of isosceles trapezoid, with longer base edges 18 of the lands 11 being opposed to longer base edges 19 of the lead terminals 21. As shown in the FIG. 4, legs or oblique edges of the each land 11 and respective lead terminal 21 are intersected with each other, while shorter base edge 28 of the each lead terminals 21 is placed within the respective land 11 when exactly placed as designed. The fillets 5 are formed along imposed-on-the-land portion of outline of the lead terminal 21. In a designed position, the longer base edge 18 of the land 11 is outwardly distanced from the shorter base edge 28 of the lead terminal 21 by 0.05 mm, while the shorter base edge 19 of the land 11 is inwardly distanced by 0.05 mm from the shorter base edge 29 of the lead terminal 21.
The structure shown in the FIG. 5 is disadvantageous because the fillet 5 becomes difficult to be recognized when position of the lead terminal 21, which is superimposed on respective land 11, is deviated in a length-wise or height-wise direction (Y direction) of the land 11 and lead terminal 21. The Y direction is perpendicular to a direction along which terminals are arranged. When the shorter base edge 28 of the land 11 is placed outward from the longer base edge 18 of the lead terminal 21, the imposed-on-the-land portion of outline of the lead terminal 21 becomes short-sized. Thus, the fringe portion for the fillet 5 becomes short-sized, to make the fillet 5 be difficult to be recognized.
When size of the lead terminal 21 is larger than that of the lands 11, in particular, the lead terminal 21 would cover the land 11 almost entirely. In this way, the imposed-on-the-land portion of outline of the lead terminal 21 would become only tiny bits along legs or oblique edges of the lead terminal 21. Thus, the fillet 5 becomes difficult to be recognized. Moreover, no visible fillet is found on shorter-base-edge-side of the land 11, on which outline of the land 11 is totally covered by the lead terminal 21. Thus, it is impossible to evaluate whether the bonding between the land 11 and the lead terminal 21 on the shorter-base-edge-side of the land 11 is good or not.
FIG. 6 shows further example of the conventional structure for connecting terminals, as designated as Prior Art 3.
In the construction shown in the FIG. 6, near-square-form rectangular lands 11 are arranged on a wiring board while planar-dumbbell-shaped lead terminals 21 are respectively superimposed on the lands 11. Each lead terminal 21 has larger length-wise dimension and smaller width-wise dimension than those of respective land 11, which are dimensions of long edges 13,14 and short edges 12 of the rectangular land 11. Along long-edge-corresponding portions 23,24 of the each lead terminal 21 both on right-hand side and on left-hand side, arc-shaped recesses 25 are formed. Thus, two short-edge-corresponding portions 22 of the each lead terminal 21 are placed outward from short edges 12 of the respective land 11. Meanwhile, the long-edge-corresponding portions 23,24 of the each lead terminal 21 are inwardly placed than the long edges 13,14 of the respective land 11. Therefore, recesses 25 both on right-hand side and on left-hand side are placed on the land 11.
Fillets 5, which are recognizable from upper side through a wiring board arranged with the lead terminals 21, are formed on long-edge-corresponding portions 23,24 including recesses 25.
The structure shown in the FIG. 6 is disadvantageous because recognition of the fillets 5 would become difficult when position of the lead terminals 21 is deviated in width-wise direction (X direction) of the lands 11 and lead terminals 21. By such deviation, on either of right-hand side or left-hand side of the lead terminal 21, the fillet 5 is formed only along a recess 25. The distance between a recess 25 and a long edge 13 becomes so small by such deviation, that recognition of the fillets 5 becomes difficult on either of right-hand side or left-hand side.
The long edges 13,14 of the each land 11 may be designed to be sufficiently distanced outward from the long-edge-corresponding portions 23,24. However, such design reduces the ratio of superimposed area for the bonding between the land 11 and the lead terminal 21 in terminals-arranging areas on wiring boards.
In view of the above drawbacks, the present invention is aimed to provide a structure for connecting terminals on a wiring board, which structure enables easy evaluation by recognition of the fillets whether bonding of terminals by solder or the like is good or not, while keeping ratio of superimposed area between terminals as sufficiently high among terminal arranging area on a wiring board or other substrate.
According to present invention, a structure for connecting terminals on a wiring board comprising: first terminals arranged on a first substrate; rectangular second terminals arranged on a second substrate and respectively superimposed on first terminals; conductive bonding means electrically and mechanically connecting each of the first terminals to respective one of the second terminals; fillets of the conductive bonding means formed along fringe portions of the each first terminal outwardly protruding from outline of the respective second terminal; a recess being formed on outline of the each first terminal and intersecting with first edge of the respective second terminal; a bump formed on the outline of the each first terminal and intersecting with second edge, opposed to said first edge, of the respective second terminal.
This feature assures a reliable recognition of fillets of the conductive bonding means that connects the first and second terminals.
The conductive bonding means is typically a solder formed of metal alloy. Nevertheless, the conductive bonding means encompasses electro conductive resin pastes, particularly electro conductive adhesives formed of highly viscous resin. The solder encompasses not only lead based ones but also silver based ones or the like and ones having relatively high melting point.
In a preferred aspect, the recess and the bump are shaped substantially as trapezoid.
In another aspect, on each first terminal, shape and size of an outline portion forming the recess are substantially identical with those of another outline portion forming the bump.
In a further aspect, with respect to one of the first terminals and another one of the first terminals next to said one of first terminals, first outline portion of said one of first terminal faces second outline portion of said another one of first terminals in such a manner that the first outline portion is substantially congruent with the second outline portion if shifted in parallel.